[Sema] Increase impact of ternary then branch aiming better diagnostics

Author: LucianoPAlmeida

lib/Sema/CSSimplify.cpp

@@ -14753,8 +14753,15 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyFixConstraint(
       // means that result would attempt a type from each side if
       // one is available and that would result in two fixes - one for
       // each mismatched branch.
-      if (branchElt->forElse())
+      if (branchElt->forElse()) {
         impact = 10;
+      } else {
+        // Also increase impact for `then` branch lower than `else` to still
+        // eliminate ambiguity, but slightly worst than the average fix to avoid
+        // so the solution which record this fix wouldn't be picked over one
+        // that has contextual mismatch fix on the result of ternary expression.
+        impact = 5;
+      }
     }
     using SingleValueStmtBranch = LocatorPathElt::SingleValueStmtBranch;
     if (auto branchElt = locator->getLastElementAs<SingleValueStmtBranch>()) {

test/expr/expressions.swift

@@ -951,3 +951,7 @@ let _ = "foo \(42 /*
 // expected-error @-3 {{cannot find ')' to match opening '(' in string interpolation}} expected-error @-3 {{unterminated string literal}}
 // expected-error @-2 {{expected expression}}
 // expected-error @-3 {{unterminated string literal}}
+
+// https://github.com/apple/swift/issues/66192
+func I66192(_: Int) {}
+I66192(true ? "yes" : "no") // expected-error{{cannot convert value of type 'String' to expected argument type 'Int'}}